October 2014

The transition from piston-engine power to turboshaft engines significantly increased the performance and operational capability of the helicopter. One of the biggest piston-engine helicopters in service was the Sikorsky S-56, powered by two Pratt & Whitney R-2800 engines rated at 2,000 horsepower each. These big round engines had to be mounted in large nacelles outboard of either side of the fuselage. Both the U.S. Marines, who initiated its development and the U.S. Army put the S-56 into service as the HR2S and the H-37 Mohave respectively. Its service career was relatively short, however.

Sikorsky won the competition to provide the Marines with a more capable replacement for the HR2S, which was to be powered by the newly qualified turboshaft engines. The S-65’s two General Electric T64 turboshaft engines, in spite of being almost 50% more powerful than the R-2800s, were much lighter and small enough to be installed immediately adjacent to the pylon housing the main transmission. The first of two YCH-53As flew on 14 October 1964. The aircraft featured a six-bladed main rotor and four-bladed tail rotor developed from those used on the S-64 Skycrane. To save space on board naval vessels, the tail boom and the rotors folded. With turboshaft engine power, it proved to be an outstanding performer, not only for the Marines but also the other U.S. military services as well as Germany and Israel. Sikorsky built 412 of the twin-engine H-53 helicopters and 110 were built in Germany.